Recovery of metal from coated metal foils



R. B. DERR Aug. 2, 1932.

1,869,886 RECOVERY OF METAL FROM COATED METAL FOILS Filed `April 9, 1931M /V/ W M4N. w l m "I M Rf.. 1 8 8m 1 8 8 Q v.//.H...|H E 0. l( H4 11NM1 .0. m 88 Q www ww Nv N wm. l wlw NH l W N I .NN M K E E m E NMM MM mw .,w mi MM.. WJ. ....N im@ 8 R .Nmil NN mw X. n @NW- 4 um Patented Aug.2, 1932 UNITED STATESv PATENT oFFvlcE RALPH IB. DERR, OF OAKMONT,PENNSYLVANIA, ASSIGNOR T0 ALUMINUM 'COMPANY 0F AMERICA, 0F PITTSBURGH,PENNSYLVANIA, A CORPORATION 0F PENNSYLVANIA RECOVERY 0F METAL FROMCOATED METAL EOILS vApplication led April 9, 1931. Serial No. 528,745.

This invention relates to the recovery -of metals from coated metalfoils, and particularly to the recovery of metallic aluminum frompaper-backed or lacquered aluminum foil.

A large proportion of the metal foils now produced is prepared for useby being coated or backed With non-metallic materials. For example, muchfoil is backed With paper attached to the foil by an adhesive. The papermay be untreated, or it maybe waxed, in Which case the Wax may act as anadhesive. The foils may be coated on one or both sides with othermaterials also, such as Wax, lacquer or varnish. Large amounts of foilscrap coated with such non-metallic materials result annually fromtrimming and similar manufacturing operations.

Attempts to recover the foils from such scrap. by Washing the paper andother nonmetallic material from these coated foils have beenunsuccessful, because complete and 'satisfactory separation could not beeffected. These coating materials are largely combustible, and attemptshave been made also to burn the paper and other combustible matter fromthe foil. This procedure as practiced prior to this invention also hasbeen quite unsatisfactory, largely because considerable amounts ofcarbonaceous matter remained With the foil, and because the residualmetal' Was burned during treatment. `Prior to my invention there hasbeen available no practical and economical means Jfor reclaiming thefoil in such scrap. Its disposition, therefore, has been a seriousproblem.

A major object of this invention is to provide a proc-ess for recoveringthe metal from backed or coated foils, -Which removes all volatile andcarbonaceous matter from the foil, avoids burning of the metal, issimple, economical, may be readily and positively controlled, provides aproduct that is clean,

bright, and of uniform quality, and is especially adapted for thereclamation Aot aluminum foil from coated aluminum foil.

A further object of the invention is to provide an apparatus foruse inthe practice of the process, which is of simple construction,

vused in the practice of the process. 'In the drawing Fig. 1 is alongitudinal sectional vlew through an apparatus adapted to carry .outthe invention; and Fig. 2 is a schematic p'lan Ivievv of agas-circulating system.-

The inventon is predicated upon my discovery that paper, adhesive, Wax,lacquers and the like non-metallic components of backed or coated foilsmay be removed readily and economically, and Withoutburnlng the foil, byfirst distilling volatile combustible matter from the backed foil byheating it in a non-oxidizing atmosphere, and then burning off residualcarbonaceous matter in an oxidizing atmosphere controlled in a mannerpresently to be described. The foil remains in a clean bright anddirectly utilizable conditon.

The process, therefore, comprises two steps, or stages. In the firststage any Wax and other volatilematter is distilled off, together withproducts ot' destructive distillation of the paper, adhesive, lacquers,Wax and the like. My tests have shown that there then remains a res'dueof carbonaceous matter, which is burned off in the second stage undercontrolled oxidizing conditions. All such 4coating materials are, torbrevity of reference, referredv to herein as volatile matter. Also,Whether backed With paper, or covered with lacquer,4 Wax, or othernonmetall'ic materials, the foils contemplated Will be referred4 tohereinafter as coated foils.

In heating such backed foil in the presence of air the combustibles, forinstance Wax and volatile matter is effected without its combustion incontact with the metal.

The invention is predicated further upon my discovery that residualcarbonaceous matter remaining after the first step may be removedwithout damage to the metal by continuing the heating while admittingair, or other oxidizing or oxygen-containing gas, so as to maintain anatmosphere of low oxygen content in contact with the metal. In otherwords, the oxidizing atmos here in this stage is controlled to burn othe carbonaceous matter without burning the aluminum..

In this stage the rate of gas supply is dependent in part upon theoxygen content of the gas supplied to the container, and upon thetemperatures of the gas and metal.

The invention is a plicable to the treatment of coated metal oilsgenerally for separation of the metal from the non-metallic coating andbacking materials. For purposes of description, and not by way oflimitation,'it will be described with particular referenceto thereclamation of metallic aluminum from paper backed aluminum foil, forwhich use the invention is especially adapted.

In the treatment of aluminum foil both steps are conducted preferably attemperatures from about 800 to 1000 F. This range of temperature issuited to most coated aluminum foils and appears to provide the shortesttreatment times consistent with 'good results. Lower or highertemperatures than these may, however, be found desirable under cer tainconditions, and for foils other than aluminum.- The temperature shouldnot exceed the melting point of the metal.

The oxidizing gas supplied in the second stage may be a1r,but my testshave shown that, in general,. the rate of iiow of pure air over the foilmust be relatively low. Relatively high rates of ow are desirable inorder to remove the heat from the foil more rapidly. Accordingly, itis'preferable to obtain the desired low oxygen atmosphere by mixing airwith an inert gas, as by usin a ue gas of controlled' oxygen content.atisfactory results are had with a ue gas containing 5 to 8 percent ofoxygen.

It is important that Athe atmosphere in the container durin the firststage of the proc- Vess be essentie y non-oxidizing. No gas need beadmitted, but it ma be found desirable tointroduce a non-oxi izing gas,such as carbon dioxide, to assist in carryin the heat to the foil mass,and more rapi y to carry off the volatile matter. Generally, inoperating as described herein, about 85 to 90 rcent of the. combustible`matter will be istilled off in the first stage.

The most satisfactory results are had by circulating the gas umform'lythrou h the mass in the second stage.' Thls is pro uctive ofuniformlypclean bright foil, and it-aids heat control, and shortcns thetreatment time. Also, the gases passed to the retort may be, andpreferably are, pre-heated for instance to about the temperature of thefoil undergoing treatment.

My tests have shown also that it is desirable to pack the foil scrap inthe container, rather than inserting it loosely. Satisfactory resultsmay be had with foil packed to a density of 0.75 to 1.25 pounds percubic foot, ilhe1 lower density being used with lighter Control of theprocess is accomplished by means of an apparatus embodying an ex'-ternally heated gas-tight retort, in which the foil is treated, andwhich is provided with means for controlling the atmosphere in contactwith the foil during treatment. Regulation of the atmosphere in thesecond stage is had most suitably by recirculation of gases fromcombustion of the carbonaceous matter in that stage.

The preferred embodiment of apparatus is shown in the accompanyingdrawing. Fig. 1 shows an apparatuscomprising a gas-tight retort 1disposed within a combustion chamber 2 built up in any suitable mannerfrom refractory and insulating brick 3 and 4 respectively.

The retort comprises a rectangular base member 5 and an upper hoodmember 6 supported in grooves formed therein in such manner as to form asubstantially gas-tight seal. To this end base 5 is provided withperipherally disposed upwardly extending flanges 8 and 8a spaced to forma groove 9 which receives the bottom of hood 6 and is filled with asealing medium, such as sand. The base is mounted on a course ofrefractory brick 3a carried by pillars 7.

The hood is open at one end for charging, and this opening is closed bya door 10. In order to exclude air from the retort during distillation,door 10 is forced by cam levers 11 against asbestos rope packing 12arranged in a groove in the door corres ending to the charging opening.A gas-tig t seal is thus formed. This door may be mounted in anysuitable manner, as for example by means of the counter-weightedmechanism shown.

The retort is fired externally by heat generated in the combustionchamber. In the apparatus shown burners 13 projecting into thecombustion chamber below the base of the retort provide the necessaryheat. These burners may use either gaseous fuel, or oil.

Removably disposed within the retort is a foil container, most suitablyin the form of a basket 14 having a foraminous base, so that gas maybeuniformly circulated upwardly through`the foil. Basket 14 is formed fromsheet metal sides and ends, suitably reinforced, and its bottom suitablyconsists of a sheet 15 of expanded metal carried on transversesupporting members 16. About the pe.-

riphery of the bottom of the basket is connected a Zbar 17 whosedepending leg extends into a groove 18 formed periherally of the retortbase by a flange 19 isposed inwardly from fiange 8a. "his groove 1s alsofilled with a sealing medium, such as sand. This construction directsgas supplied below the basket `upwardly through its contents in a mannerproductive of the best results. 1

The atmosphere in the retort is controlled by gas supplied from `amanifold system carrled by the retort base below the basket. Theembodiment shown comprises headers 2O and 20a disposed longitudinally ofthe sides of the retort base and connected at one end to a gas supplyline 21. The headers are connected by a parallel series of transversepipes 22 perforated along their under s1dc s to effect properdistribution of the gas uniformly over the entire area defined by thcbottom of they basket.

Volatile matter distilled from the foil, and gaseous products ofcombustion formed 1n the second stage ofthe process pass from the retortinto a. 2-Way valve 23 havng branches 24 and 25. Branch 24 is connectedto a flue 26 which leads to a stack 27, Fig. 2, and the other branchleads to a conduit 28 connected at one end to flue 26 and at the otherend to a manifold 29 leading to gas lines 21. Products of combustionfrom burners 13 in the combustion chamber are withdrawn to flue 26 by aconnection 30, Fig. 1.

The units just described permit of reclamation of foil in accordancewith this invention. These units may be used singly. or a number may bebuilt up into a combined struct-ure, as indica-ted schematically in Fig.2. The construction of the heating chamber or retort is such as toprevent any substantial leakage of air into it, and this is important ineffecting the distillation stage. Control of the atmosphere in theretort thus is easy. During combustion of carbonaceous matter in thesecond stage-of the process the Hue gases contain carbon dioxide. In thepreferred practice these gases are recirculated as a convenient means ofcontrolling the oxidation in the manner set forth.

Such recirculation may be had by the piping layout shown in Fig. 2, fora three unit apparatus. The units are indicated by the letters A, B andC. The products of combustion or distillation, as the case may be,

pass from the retorts to valves 23. Assuming that units A and B areoperating in the second stage of the process, that is in the burningoifofcarbonaceous matter in a con trolled oxygen-containing atmosphere,these units will require a mixture of flue gas and air in controlledproportions. Valves 23 vof these two units are turned to direct.v theprod- -scribed is entirely freed from the backing ucts of combustioninto conduit 28, as shown by the arrows, Fig. 2. A portion of the gasesflow to flue 26 and thence to the stack, another portion being drawnfrom conduit 28 by a blower 31. Air is also drawn into the blowerthrough an inlet 32 in proportions adapted to provide the desired Huegas-air mixture. Such controlv may be effected by means of a CO2recorder controller indicated conventionally by the numeral 33. Thisrecorder controller may be of any of the well known types, it beingmounted in manifold 29 and controlling` a valve in the air inlet. Themixture of flue gas and air is passed by the blower to manifold 29.Valves 34 at each unit control flow from the manifold to gas lines 21.Valves 34 in units A and B are opened, and the gas mixture isdistributed through headers 2O and pipes 22 to the retorts.

Unit C is being used in the first, or distillation stage. The wax andother combustible matter may be permittedgto burn outside of the retort.Preferably, however, the volatile products are drawn off through branch24 and passed to stack 27 through flue 26. The wax may be separated fromthese gases, if desired, by an appropriate condenser 35. During thisstage valve 34 for unit C is closed. In case the "olatile product-s areburned, this may be done by pcrforating the top of the retort andpermitting the gases to burn in the furnace chamber outside of theretort.'

Such operation will provide sufficient heat to complete distillation,burners 13 being extinguished after the products have started to burn.Furthermore, by the use of a. furnace of sufficient heat capacity. thechambers might be hot enough, after the first stage of the treatment, tomaintain suitable temperatures throughout the second stage of thetreatment, and to start distillationin an immediately followingtreatment. Thus, y by suitable design of furnace and control of itscontinuous operation, the heat derived from the products of combustionmay be so conserved that the supply of external heat becomes unnecessaryonce the furnace has been put into operation.

Tests made with an appara-tus similar to that described have shown thatpractically all aluminum foils may be recovered satisfactorily bypacking them to about the densities described in beds of from two tothree feet deep, and heating to about 800 to 1000 F. The first stageusually requires about one and one-half to two hours. Using in thesecond stage a mixture of Hue gas and air containing from about 5`to 8%of oxygen, preheated to about 800 to 1000 F. and passed through the foilat a rate varying from about 0.25 to 0.6 cubic foot per squarefoot ofsurface per minute, this step generally requires about four to sixhours.

Backed foil treated in the manner just dematter, and it is of bright,clean and uniform quality. At times the foil may contain small amountsof a loose fluffy ash. Such ash may be readily separated from the foilby screening or aerating.

According to the provisions of the patent statutes I have explained theprinciple and mode of operation of my invention and have illustrated anddescribed what I now consider t0 represent its best embodiment. HOW-ever, I desire to have it understood that, Within the scope of theappended claims, the invention may be practiced otherwise than asspeciiically illustrated and described.

I claim:

1. A process of treating coated metal foil to recover the foil,comprising distilling vo1 atile matter from the coated foil by heatingit in a non-oxidizing atmosphere, and then burning olil carbonaceousmatter in an oxidizing atmosphere controlled to burn said carbonaceousmatter but not the metal.

2. A process of treatingr coated metal foil to recover the foil,comprising heating the coated foil in a non-oxidizing atmosphere todistill oi the major portion of the volatile matter, and continuing theheating While circulating a gas of low oxygen content uniformly over thefoil at a rate such as to burn off only residual carbonaceous matter.

3. A process of treating coated metal foil to recover the foil,comprising distilling off the major portion of the volatile matter byheating the backed foil at a temperature be- 10W the melting point ofthe metal in a nonoxidizin'g atmosphere, and then burning off theresidual carbonaceous matter by heating in an atmosphere of Hue gascontaining oxygen regulated in amount to burn oii' only residualcarbonaceous matter.

4. A process of recovering metallic aluminum from aluminum foil coatedwith nonmetallic combustible material comprising distilling oif volatilematter in a non-oxidizing atmosphere at an elevated temperature belowthe melting point of aluminum, and then supplying oxygen for combustionof residual carbonaceous matter, the oxygen concentration being adjustedto effect such combustion Without burning the aluminum. 5. A process oftreating paper-backed aluminum foil to recover the foil, comprisingdistilling off the major portion of the volatile matter between 800 to1000O F. in a non-oxidizing atmosphere, and then supplying oxygen forCombustion of the residual carbonaceous matter, the oxygen concentrationbeing adjusted to effect such combustion Without burning the aluminum.

6. A process of recovering metallic aluminum from aluminum foil coatedWith nonmetallic combustible material comprising distilling ofi' themajor portion of the volatile matter by heating the coated foil in anon-oxidizing atmosphere at a temperature below the melting point ofaluminum, and

then burning o residual carbonaceous matter by continuing the heating inan atmosphere of flue gas containing oxy en regulated in amount to burnoi residuacarbonaceous matter without burning the aluminum.

7. A process of 4treating paper-backed aluminum foil to recover thefoil, comprising heating the backed foil at about 800 to 1000 F. in anon-oxidizing atmosphere to distill 0H the major portion of volatilematter, and then burning oil residual carbonaceous matter by heating at800 to 1000o F. in an oxidizing atmosphere containing about 5 to 8% ofoxygen and sup lied at a rate such as to prevent burning o the aluminum.

8. A process according to claim 4, the oxygen content in said flue gasatmosphere being about 5 to 8%.

9. A process of treating paper-backed metal foil to recover said foilcomprising heating the backed foil at a temperature below the meltingpoint of the metal in a nonoxidizing atmosphere to distill oi the majorportion of volatile matter, then supplying air to burn off residualcarbonaceous matter, and mixing said air with gases from combustion ofsaid carbonaceous matter to restrict the combustion to said carbonaceousmatter.

l0. A process of treating paper-backed aluminum foil to recover thefoil, comprising packing the backed foil in a container to a density ofabout 0.75 to 1.25 pounds of foil per cubic foot, heating the thuspacked foil in a non-oxidizing atmosphere to distill off volatilematter, and then burning ofi' residual carbonaceous matter in anoxidizing atmosphere controlled to burn said carbonaceous matter but notthe aluminum.

In testimony whereof, I sign my name.

RALPH B. DER-R.

iii

